A. Field of the Invention
This invention relates to an improvement in a spin-texture process and, more particularly, to the process described in U.S. Pat. No. 4,202,854 for producing monocomponent polyamide yarn having latent crimp. The improvement provides for increased polymer throughput rates without sacrificing the amount or uniformity of the bulk resulting from development of the latent crimp.
B. Description of the Prior Art
U.S. Pat. No. 4,202,854 relates to a spin-texture process for producing multifilament polyamide yarn having a helical latent crimp. The process comprises extruding molten polyamide through a spinneret at a given rate (i.e. throughput) to provide a monocomponent multifilament yarn that is quenched, passed around a feed roll (e.g. driven feed roll and its associated idler roll) with a given number of wraps, and drawn as it leaves the feed roll. The filaments are subsequently collected, for example, by being wound onto a bobbin. The process is characterized in that the feed roll is heated to a temperature between 100.degree. C. and 175.degree. C., the filaments are drawn at a draw ratio ranging from greater than 1.0 and less than 4.0 (e.g. 1.25 to 3.25), and the throughput, temperature of the feed roll, number of wraps taken by the yarn around the feed roll, and draw ratio are correlated to provide a yarn having an optimum amount of bulk upon development of the latent crimp. It is desirable for economic reasons that the process be operated at the highest possible polymer throughputs. Unfortunately, the process described in the patent is "throughput limited", that is, for any given spinneret there is a maximum throughput, beyond which the latent crimp imparted to the yarn by the process and, therefore, the bulk level of the yarn upon development of this latent crimp fluctuates and cannot be controlled. At throughputs below this maximum throughput unexpected fluctuations in the latent crimp (and bulk level) can easily be controlled (eliminated) by changing processing conditions, e.g., feed roll temperature, draw ratio, etc. For commercial operations, the bulk level of the yarn must be capable of being controlled within relatively narrow limits so as to avoid wide variations in bulk along the length of the yarn. Another problem encountered in operating the process at high throughputs is that the bulk level of the resulting yarn upon development of the latent crimp is too low (i.e., below 20%) for certain carpet yarn applications.